Cable ties are elongated devices used for holding a plurality of items or bundles of strand materials, such as tubes, wires or cables together. Cable ties are generally molded of plastic material and have a head and an integrally connected strap terminating in a free end or tail. The head includes an opening for progressive insertion of the tail and strap and houses a pawl integrally hinged in the head opening for engaging and gripping the strap. The pawl is formed with a plurality of transversely extending teeth which ratchet over a rack of teeth on the strap as the strap is pulled through the head opening and tightened around the tied items.
Various prior examples of such cable ties may be found in the U.S. Pat. No. 3,605,199 to Eberhardt and U.S. Pat. Nos. 4,788,751 and 4,897,899 to Shely et al., all of which are assigned to the same assignee as the present invention.
Cable ties are useful for a wide variety of purposes from tying bundles of wires and cables together, as the name implies, to securing packages and aligning and/or suspending tubes, pipes, conduits or other elongated items in their housings or supporting frameworks. Frequently, cable ties are employed during initial installation of various components and then become rather inaccessible for later repair or replacement. Also, the environment in which cable ties are used is often detrimental to their life. Conditions such as heavy loading, vibration and fluctuations in temperatures and humidity frequently place severe stress on the cable ties and the materials from which they are made.
As may be seen in the above-noted U.S. Pat. No. 3,605,199, the strap of the cable tie disclosed there has its minimum material thickness (i.e. is the thinnest) at the root of each tooth of the rack of teeth formed on the cable tie strap. Moreover, the strap loading is applied to the abutting faces of the rack teeth immediately adjacent the root section of an adjoining tooth. This loading not only applies a tensile stress to the strap at its weakest point but the offset forces on the teeth also apply a bending moment right along the sharply defined transverse line which forms the juncture of one tooth root with the adjacent tooth face. The concurrence of all of these factors; thinnest material, tensile and bending forces and sharply defined material transitions having a substantially linear direction, not only tend to produce stress fractures, but also, to rapidly propagate them along these transverse lines of weakness.